1. Field of the Invention
The present invention relates to a transformer, and more particularly, to a transformer having an integrated passive device (IPD) used in a complementary metal-oxide semiconductor (CMOS) power amplifier.
2. Description of the Related Art
In general, at a transmitting terminal of a mobile communication terminal such as a mobile phone, a power amplifier is used to amplify power of a transmission signal. The power amplifier should amplify the transmission signal by appropriate power. As methods of controlling output power of a power amplifier, there are a close loop method in which a part of an output signal is detected via a transformer at an output terminal of the power amplifier and the signal is converted into a direct current (DC) by using a Schottky diode and compared with a reference voltage using a comparator and an open loop method of sensing a voltage or a current applied to the power amplifier and controlling power.
The closed loop method, which is generally used, has an advantage of precisely controlling power and a disadvantage of decreasing efficiency of the amplifier due to complexity of embodying a circuit and a loss caused by a coupler. The open loop method, which has a simple circuit structure and is generally used now, is incapable of precisely controlling power.
Recently, as elements used in the closed loop method are integrated as an integrated circuit (IC), it is simple to embody a circuit. Also, since performance of a control chip is improved, a coupling value of a directional coupler is greatly decreased, thereby greatly reducing a loss due to the directional coupler. Particularly, to a global system for mobile communication (GSM) in which a ramping profile is important, the close loop method capable of precisely controlling power is applied.
Researches to embody an effective transformer controlling an output of a power amplifier have been continuously performed. However, there are problems in which harmonics components occur in an output signal and the size of coupling varies with a location of a power supply pad when embodying a transformer.